(1) Field of the Invention
The present invention relates to a revolution increase-decrease determination device which determines whether the number of engine revolutions of a nearby vehicle is increasing or decreasing, on the basis of an engine sound emitted from the nearby vehicle.
(2) Description of the Related Art
Conventional technologies for determining conditions of a nearby vehicle include the following example.
Japanese Unexamined Patent Application Publication No. 2000-99853 discloses a technology whereby: an ambient sound is converted into a sound pressure level signal; an absolute level of the sound pressure level signal in a specific frequency band is compared with a reference level to determine the presence or absence of a nearby vehicle; and, based on temporal fluctuations in the sound pressure level signal, it is also determined whether the nearby vehicle is approaching or not. This technology is referred to as the first conventional technology hereafter.